Carbon fiber strengthened speaker cone

ABSTRACT

A novel speaker diaphragm having a high specific modulus for use in conventional loudspeakers including the magnetic and electrostatic type loudspeakers, the diaphragm comprising a carbonaceous fibrous web impregnated by a resin. The speaker diaphragm has a sonic velocity that is comparable to or exceeds that of a speaker diaphragm made of aluminum.

United States Patent Boszor Dec. 30, 1975 CARBON FIBER STRENGTHENED 3,073,916 1/1963 Williams et al. 179/181 R X SPEAKER CONE 3,367,812 2/1968 Watts 3,539,296 11/1970 Selke [75] Inventor: Samuel M. Boszor, Parma, Ohio 3,668,336 6/1972 Wright [73] Assigneez Union Carbide Corporation, New 3,671,385 6/1972 Trent et a1. 423/447 X York, NY. Primary Examiner--Thomas W. Brown Flled? p 1973 Attorney, Agent, or Firmlsrael Blum App]. No.: 399,319

US. Cl. 179/181 R; 181/169 Int. Cl. H04R 7/26 Field of Search 179/181 R, 111 R, 115 R;

References Cited UNlTED STATES PATENTS 3/1961 Supitilov 179/181 R X 57 ABSTRACT 11 Claims, No Drawings CARBON FIBER STRENGTHENED SPEAKER CONE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to loudspeakers and more specifically to speaker diaphragms having a high specific l modulusfor use in magnetic or electrostatic loudspeakers, the diaphragms comprising a carbonaceous fibrous web impregnated by a resin.

2. Description of the Prior Art Loudspeakers are an integral part of sound reproduction systems. Conventional loudspeakers include electrostatic and magnetic loudspeakers. An electrostatic or condenser loudspeaker is fundamentally a huge capacitor and generally comprises a conducting diaphragm situated in a polarized field. Sound is produced when an audio signal is induced onto the diaphragm, the capacitors inner plate, which modulates the polarized voltage, causing the diaphragm (inner plate) to be both pushed and pulled between two outer, fixed immovable electrodes in accordance with the signal. Heretofore, the flexible, conductive diaphragm has generally consisted of a nonconducting material coated with thin conducting material having a high degree of resistance, e.g., a very thin plastic film with a conducting metallic coating.

A magnetic or driving coil loudspeaker comprises a voice coil, diaphragm and suspension system. An electromagnetic motor transforms an audio signal into a vibrating diaphragm, the diaphragm being conically shaped to maximize mechanical stability. The vibrating surface of the diaphragm compresses air into motion (sound waves) which we recognize as sound.

Rigidity and lightness are two competing requirements in the design parameters of a conical diaphragm. A high modulus of elasticity optimizes the diaphramss ability to function with piston-like movements and not break up into separate vibrating sections. Low mass is desired in order than the inertia of the diaphragm be low. Conical diaphragms have been composed of various materials, including metal, cellulose paper, plastic, cloth, wool and expanded polystyrene. However, it was apparent that no material previously attempted was ideal nor did it provide the proper balance between mechanical stability and acoustic performance.

Cellulose paper has long been a standard compromise between quality and economics in moving coil loudspeakers, providing a reasonable balance between mechanical stability and acoustical performance. However, it is known that even a quality Kraft paper impregnated with a stiffening resin has a maximum sonic velocity of only about 2.5 X I0 cm/sec. By sonic velocity of paper is meant the square root of the ratio of its Young's modulus to its density. Sonic velocity aids in analyzing the extent to which a conical diaphragm simulates ideal piston-like motion. Increasing the sonic velocity not only decreases frictional energy losses in the diaphragm produced from out of phase vibrational patterns and corresponding cancellation effects that result therefrom, but also increases high frequency response. Consequently, the sonic velocity of a diaphragm is a measure of the limits in the crispness of transient responses and range of linear frequencies the diaphragm may provide.

Because a higher specific modulus than possessed by the finest resin impregnated cellulose paper was desired, metals such as aluminum were attempted even though they had other defects. Aluminum, for example, provided a speaker diaphragm having a sonic velocity about twice that obtainable with cellulose paper, but the diaphragm required reinforcing joints to dampen circumferential vibrations associated with its inherent thinness. Anodising the aluminum diaphragm increased its maximum sonic velocity to about four times that obtainable with cellulose paper.

SUMMARY OF THE INVENTION It is an object of this invention to provide a loudspeaker diaphragm comprising a carbonaceous fibrous web impregnated by a resin, the diaphragm having a high specific modulus of elasticity and a sonic velocity comparable or better than aluminum diaphragms. Another object of this invention is to provide a loudspeaker diaphragm comprising a carbonaceous fibrous web impregnated by a resin, the diaphragm having a sharper transient response and wider frequency range than cellulose paper. An object of this invention is to provide a woofer diaphragm comprising a carbonaceous fibrous web impregnated by a resin, which diaphragm is capable of reproducing a wider frequency range than comparable paper woofer diaphragms. A further object is to provide an electrostatically driven speaker diaphragm comprising a conductive carbonaceous fibrous web impregnated by a resin.

Briefly, this invention relates to a diaphragm for use in an electroacoustical device, the diaphragm comprising a carbonaceous fibrous web impregnated by a resin. The diaphragm of this invention is characterized by having a high specific modulus and sonic velocity.

The term specific modulus as used throughout the specification unless otherwise indicated, should be understood to equal the modulus of elasticity (Youngs modulus) divided by the basis weight of the material, ie its weight per unit area.

The term impregnated as used throughout the specification and unless otherwise indicated, should be understood to signify the result of impregnating and/or surface coating the carbonaceous fibrous web with a resin. It does not necessarily imply that all, or even a major proportion of the interstices or other voids of the carbonaceous fibrous web must be filled or covered with resin. However, it is preferred to have the resin adhering or clinging to a major portion of the fibers of the carbonaceous fibrous web.

Individual filaments of carbon fiber which are useful in forming a diaphragm material are known to have a range of moduli extending from about 10 million psi to about 100 million psi and a maximum density of about 2 gm/cm. A carbonaceous fibrous web of this invention may be formed using these fibers and impregnated by a resin. It is possible for the diaphragm of this invention to reach a fiber loading of between about 30% to about carbon fibers by volume, the balance being a resin. Preferably, diaphragms having a fiber loading between about 60% to about 70% carbon fibers by volume, the balance being a resin will be used in this invention. Moreover, the carbonaceous fibrous web impregnated by a resin which is used as the diaphragm material of this invention may have a maximum density of about l.7 gm/cm and a maximum modulus of elasticity of about 30 million psi. Preferably, a carbonaceous fibrous web impregnated by a resin useful in this invention should have a modulus of elasticity varying from about 3 million psi to about 30 million psi and a density varying between about 0.8 gm/cm and about 1.7 gm/cm respectively.

The diaphragms of this invention should have sonic velocities that exceed the maximum sonic velocity of a high quality, resin impregnated, cellulose paper diaphragm and equal or exceeding even aluminum diaphragms. Loudspeaker diaphragms comprising a carbonaceous fibrous web impregnated by a resin are characterized by having sonic velocities between about 2.5 X 10 cm/sec and about 1 l X cm/sec, based on available test data, the examples reported hereinafter and theoretical expectations. Preferably, a diaphragm comprising a carbonaceous fibrous web impregnated by a resin and having a sonic velocity greater than about 2.6 X 10 cm/sec and more preferably greater than about 4.6 X 10 cm/sec should be used in connection with this invention. Even more preferably, the I sv sv wherein SV is the sonic velocity of the diaphragm of this invention and SV is the sonic velocity of an aluminum diaphragm.

Moreover, based on available test data and theoretical expectations, a carbonaceous fibrous web impregnated by a resin and useful in this invention may have a modulus of elasticity between about 4.4 X 10' dynes/cm and about 220 X 10 dynes/cm preferably between about X 10 dynes/cm and about 220 X 10 dynes/cm More significant a characterizing property of the diaphragm of this invention is its specific modulus of elasticity. Indeed, the diaphragm of this invention preferably has a specific modulus of elasticity which may be defined by the formula wherein SM, is the specific modulus of elasticity of the diaphragm of this invention and SM is the specific modulus of elasticity of an aluminum diaphragm.

The diaphragm of this invention, moreover, possesses both a higher specific modulus and sonic velocity when compared to the finest cellulose paper. As a result of having a higher specific modulus and sonic velocity, the diaphragm comprising a carbonaceous fibrous web impregnated by a resin may follow higher frequencies than a cellulose paper diaphragm of the same shape, size and weight. Preferably, the specific modulus and sonic velocity of the diaphragm comprising a carbonaceous fibrous web impregnated by a resin is also comparable or superior to the finest aluminum diaphragms. Furthermore, it is possible for the transient response of the diaphragm of this invention to be sharper than a comparable cellulose paper diaphragms due to its superior specific modulus.

High modulus, high strength carbon fibers suitable for use in this invention may be prepared as described in US. Pat. Nos. 3,412,062; 3,503,708 and 3,529,934. The carbon fibers when cut to a size suitable for process may be employed in the instant invention. Carbonized or graphitized pitch this invention.

The carbonaceous fibrous web preferably employed in this invention may be prepared by processing carbon fibers by any method, either wet or dry, which effects the dispositiono f such fibers in intimately contacting relation in a fibrous body. Air laying operations such as carding and garnetting which effects a relatively oriented disposition of fibers into a paper sheet are suitable for this purpose.

A carbonaceous fibrous web impregnated by a resin is the preferred fabric for use in this invention. Preferably, a carbon fiber sheet or paper may be prepared by water laying short carbon fibers using well known paper making techniques. A carbonaceous fibrous web isalso preferably prepared by collecting pitch fibers and forming them into a carbonaceous fibrous web. More preferably, a non-woven carbonaceous fiber web may be resin impregnated, shaped by well known techniques and the resin cured, forming a shaped diaphragm.

When preparing a paper by the water laying of carbon fibers, the fibers are first cut or chopped to a size suitable for processing, e'.'g., about %'inch in length; homogeneously intermixed with water and a suitable binder, such as starch or other well known binder, to form an aqueous slurry; then deposited from the slurry upon a substrate such as a flat sieve of fine mesh which retains the fibers to form a sheet. This sheet is then processed by conventional paper making techniques to produce the final carbonaceous product.

Converting the carbon fiber slurry into sheets of carbon fiber paper involves three. general steps, or modifications of these, by which commercial base papers are made:

1. The arrangement of the fibers in the slurry into a wet sheet;

2. The removal of a portion of the free water from the wet sheet by wet pressing this is reflected by improved physical characteristics of the paper;

3. The progressive removal of additional water by heat.

A wet sheet is generally formed either by running a dilute suspension of carbon fibers evenly onto the surface of a moving endless belt of wire cloth, through which excess water may be drained, or by running an endless belt of wire cloth through a suspension of carbon fibers. In the first case the Fourdrinier process part of the water drains off by gravity, a part is taken from the sheet by suction, and a part is removed by pressure; in the second case, a vacumm is maintained below the stock level in the cylinder in which the wire cloth is rotating and the sheet forms on the wire by suction much as does a cake on a vacuumfilter. Generally, most paper grades are formed by the'first process. In either case, the thickness of the sheet is controlled by the speed of travel of the machine, by the consistency (ratio of fiber to water) of the suspension, or by the amount of stock allowed to flow onto the machine.

After the carbon fiber sheets have been prepared as described hereinabove, they are physically processed, e.g., cut into a predetermined shape for assembly into aconically shaped diaphragm. A loudspeaker diaphragm typical of this invention may be constructed with paper prepared from artificial or natural carbon fibers having a diameter between about 3 pm and about 15 um, and preferably between about 4 pm and about 8 p.rn. Moreover, the diaphragm may have a modulus exceeding fibers may also be employed in about 3 million psi and preferably exceeding about million psi and more preferably exceeding about million psi. I

Furthermore, a non-woven carbonized fiber web made from chopped or blow spun. staple fibersmaybe used as the precursor to the speaker diaphragm of this invention. The non-woven carbonaceous web may be impregnated with a suitable resin such as an epoxy, furane, phenolic, melamine or the like. Thereafter, the web may be physically processed in a conventional manner to form a shaped web which shape the diaphragm will have. The resin impregnated web may then be heated a predetermined time at a temperature sufficient to cure the resin and maximize the diaphragm stiffness. This heat treatment may be combined with the shaping step, if desired.

Alternatively, a diaphragm typical of this invention may be formed by blowing carbonized staple fibers onto a preshaped screen. A vacuum is created behind the screen to assist collecting and binding the staple fibers together into a carbonaceous fibrous web. A binder dissolved in a solvent is preferably added to the staple fibers during this process. Preferably, the binder used is a resin such as an epoxy, furane, phenolic, melamine or the like dissolved in such solvents as acetone, toluene, benzene, methyl ethylketone or the like. Those skilled in the art will readily appreciate that the diaphragm may be directly formed in the above manner without need for further processing, the diaphragm having the shape of the preshaped screen.

Adding a binder not only joins the fibers together, but strengthens the carbonaceous fibrous web. Whether the binder such as a carbonizable resin is added during the carbonaceous fibrous web making process or applied as a coating to a finished carbonaceous fibrous web, it should be heated to a temperature sufficient to cure the resin and maximize stiffness of the web. Carbonizable resins which stiffen the carbonaceous fibrous web as described hereinabove include phenolic, epoxy, furane and the like.

In one embodiment, a diaphragm typical of this invention may be varied in shape. For example, it may be conical in shape or conically shaped near the apex of the cone. Furthermore, by any one of several conventional physical or machining methods such as a molding process and the like, a diaphragm typical of this invention may be provided with circumferencial, annular or sinusoidal shaped annular corrugations and the like.

In another embodiment, a diaphragm typical of this invention may be uniform in thickness or graduated, if desired at one end. A thickness of between about 0.005 inch and about 0.025 inch is employed for a diaphragm used in magnetic loudspeakers.

In still another embodiment, a diaphragm as described in this invention may be used in any one of several magnetic loudspeakers commonly employed. For example, the magnetic loudspeaker may employ multiple small conical diaphragms or conical diaphragms in sealed enclosures or conical diaphragms at the end of tubes. As is readily appreciated by those skilled in the art, improved magnetic loudspeakers of various shapes, dimensions and designs having superior tone qualities and frequency ranges can be produced employing diaphragms typical of this invention.

Moreover, while a diaphragm typical of this invention may be used to reproduce the entire audible range, i.e., from about 20 to about 20,000 HZ (cycles per second it is preferable, in certain instances, to employ a combination of several speakers in a sound reproduc- 6 tion system each accuratelyreproducing only limited bands within the audible frequency range. As is readily understood by those skilled in the art, a diaphragm in accordance with this invention may be used in a woofer loudspeaker which generally reproduces the bass range of audible frequencies.

- Furthermore, an electrostatic speaker dia phrag typical of this invention comprises a carbonaceous fibrous web impregnated by a resin. The results of the examples described hereinbelow illustrate the electric conductivity of the carbonaceous fibrous web impregnated by a resin. Being electrically conductive, the carbonaceous fibrous web impregnated by a resin not only fulfills the conductivity requirement of an electrostatic speaker diaphragm but also eliminates the need for applying a surface coating to make the electrostatic speaker diaphragm conductive as is now done.

The material employed for the electrostatic speaker diaphragm may be formed of a resin impregnated fibrous web and range in thickness from about 0.005 inch to about 0.01 inch. Preferably, a thickness of about 0.007 inch is employed. An electrostatic speaker diaphragm manufactured according to the teachings set forth herein can compare favorably with the linearity of frequency response curves of electrostatic speaker diaphragms consisting of conventional materials having comparable types of construction and capabilities.

EXAMPLE Four epoxy resin impregnated sheets having a fiber loading of approximately 55% and four phenolic resin impregnated sheets having a fiber loading of approximately 60% were prepared for testing purposes. At the outset, two pieces each of four different carbon fiber mats were obtained. Two of the mats were blow spun, staple fiber mats, Grades VM0032 and VM0033 (commercially available from Union Carbide Corporation, Carbon Products Division, New York, N.Y.). The third was a VFB paper which is basically a low twist, rayon base, carbon yarn which has been carbonized at 700C., chopped into staple fibers and made into a paper using the Fourdrinier process. The fourth was a carbon fiber mat having 16 inch staples, produced from melt spinning of pitch and subsequentheat treatment at 1400C. In addition a resin impregnated cellulose paper was obtained from a 6 X 9 inch Utah RC 69 D speaker diaphragm (commercially available from Utah Electronics, Huntington, 1nd.).

In preparing the epoxy resin impregnated sheets, one of each of the four different mats described hereinabove was cut into eight inch square samples. Then, the samples were immersed in Bakelite epoxy resin ERLB- 4617 (commercially available from Union Carbide Corporation, Plastics Division, New York, NY.) to which 50 p.p.h. Tonox hardener (commercially available from Naugatuc Chemical Co., Division of Uniroyal, Naugatuc, Conn.) had been added. The samples were each laid on release coated aluminum foil and allowed to age 3 to 5 days. A pair of each of the samples was placed between aluminum foil in a heatable press and heated to C. under lightcontact pressure for /2 hour. The samples are close pressed until each sample was approximately 0.01 inch thick and held still /z hour at 100C. The temperature was raised to C. and held there for 2 hours, and then was raised to C. and held there for 2 additional hours. The samples were cooled under pressure and removed from the press at 120C.

7 With respect to the phenolic resin impregnated sheets, the remaining four different mats described hereinabove were prepared for testing purposes as follows: A Bakelite BLS3536 phenolic resin (commer- 8 following procedure: Strips /2 inch wide and inches in length were cut from the samples. The weight, area and thickness of each strip was determined to calculate the density of each sample. Resistivity of each sample was cially available from Union Carbide Corporation, Plas- 5 obtained by running 1 ampere current from a constant tics Division, New York, N.Y.) was mixed with 3 p.p.h. current supply through a cm. length of each sample dimethyl sulfate catalyst and sufficient acetone to thin and measuring the voltage drop with a digital voltme- (approximately 5 parts acetone per 1 part resin). The ter. Lastly, to obtain tensile strength, modulus of elasresm was spread upon each mat sample using a paint ticity and sonic velocity, the samples were each loaded brush to apply 130 p.b.w. resin to 100 p.b.w. carbon 10 in an instron Table Model Test Machine with airflbers. The samples were allowed to air dry overnight activated rubber faced grips and a 200 lb. load cell. The and then were cut into 7 inch square pieces. The samsamples were broken with guage lengths of 1 and 4 ples were then molded in a steel mold using silicone inches at a cross head speed of 0.05 inches per minute release paper to separate plies at a pressure of 1000 psi and tensile strength, modulus of elasticity and sonic and temperature of 125C. for minutes. The samples 15 velocity were calculated from head speed values and were then removed from the press. chart rates. Results of the above-mentioned tests are The epoxy impregnated sheets, phenolic impregsummarized in Table 1 as follows: nated sheets and Utah paper were each tested using the TABLE I Utah Paper Epoxy impregnated VMOO32 Basic Weight gm/cm .00918 .034 Density gm/em .452 1.247 Tensile Strength psi min. max. avg. min. max. avg.

1900 4460 3000 3538 13537 9212 Tensile Strength dyries/em 2.07X10 6.4 10

min. max. avg. min. max. avg. Modulus of Elasticity psi 1.9X10 5.3X1O 3.4X10 15X10 10 23X10 Modulus of Elasticity 2.3X10 16Xl0 dynes/cm min. max. avg. min. max. avg. Specific Modulus of Elasticity si/gm/em t.8 10 5.8X10 3.7 10 44x10 74x10 6.8 t0 Sonic Velocity cm/sec. 2.2)(10 3.6)(10 Resistivity ohm/cm 180 10" Phenolic impregnated VMOO32 Epoxy impregnated VM0033 Basic Weight gm/cm 0.0254 .025 Density gmlcm .834 1346 min. max. avg. min. max. avg. Tensile Strength psi 423 i034 780 3367 1 1 186 6620 Tensile Strength dynes/cm .54X10" 4.6X10" min. max. avg. min. max. avg. Modulus of Elasticity psi 12Xl0 39Xl0 28x10 27 1O 10 34X1O Modulus of Elasticity dynes/cm 19 10 23X10 min. max. avg. min. max. avg. Specific Modulus of Elasticity psi/gm/em 4.7 10' 15x10 11x10 10.8X10 18X10" 14 10 Sonic Velocity cm/sec. 4.8Xl0 4.2Xl0 Resistivity ohm/cm 1230 10" 93 10 Phenolic impregnated Epoxy impregnated VM0033 VFB Paper Basic Weight gm/cm 0.0232 .029 Density gm/cm" 1.302 1.067

min. max. avg. min. max. avg. Tensile Strength dynes/em 900 1515 1320 3345 12509 8186 .91X10 5.6Xl0" min. max. avg. min. max. avg. Modulus of Elasticity psi 42 l0 58X10 X10 7.S 10 10.5)(10 9.310" Modulus of Elasticity dynes/em 34X10" 6.4 10

min. max. avg. min. max. avg. Specific Modulus of Elasticity psi/gm/Cm lXXlO" 25X10" 22Xl0 2.6Xl0" 3.6 10 3.2 l0 Sonic Velocity cm/sec. 5.1)(10 2.4X10 Resistivity ohm/em 147x10 254x10" Phenolic impregnated Epoxy impregnated 16 inch VFB Paper Staple Mat Basic Weight gm/em 0.0230 .056 Density gm/cm .346 I 1.108

min. max. avg. min. max. avg. Tensile Strength psi 163 619 340 1196 12690 8132 Tensile Strength dynes/em" .23X10" 5.6X10" min. max. avg. min. max. avg. Modulus of Elasticity .75 10"' 2.4X10" l.4 10" l8 10 26 10 23Xl0 PS1 Modulus of Elasticity TABLE l-continued Utah Paper Epoxy lmpregnated VM0032 dyncs/cm .96Xl'" I6Xl0'" min. max. avg. min. max. avg. Specific Modulus of Elasticity psi/gm/cm .33Xl0 LOX l0 .6lXl0" 3.2)(10 4.6 10 4.lXl0 Sonic Velocity cm/scc. l.7Xl0 3.8Xl0 RResistivity ohm/cm 563000Xl0" l34Xl0 Phenolic lmpregnated l6 lnch Staple Mat Basic Weight gm/cm 0.0200 Density gm/cm l.l705

min. max. avg. Tensile Strength psi 2309 3264 2770 Tensile Strength dynes/cm 1.9Xl0

min. max. avg. Modulus of Elasticity psi 3.7Xl0 7.3Xl0 5.5Xl0" Modulus of Elasticity dyncs/cm 3.8 l0

min. max. avg. Specific Modulus of Elasticity psi/gm/cm 1.8X 3.7XI0 2.8Xi0 Sonic Velocity cm/sec. 1.8Xl0 Resistivity ohm/cm 160Xl0 Those skilled in the art will appreciate that the particular embodiments of the invention described hereinabove are intended to be illustrative only and are not intended to limit the scope of the invention.

What is claimed is:

1. A loudspeaker diaphragm, said diaphragm consisting essentially of a carbonaceous fibrous web of carbon fibers and a resin, said carbon fibers representing between about and about 70% by volume of said diaphragm, the balance being said resin, said diaphragm having a Young's modulus between about 3 million psi and about 30 million psi and a density between about 0.8 gm/cm and about 1.7 gm/cm so as to provide a sonic velocity for said diaphragm between about 2.5 X 10 cm/sec and about ll X 10 cm/sec.

2. A diaphragm as defined in claim 1 wherein said carbon fibers are staple carbon fibers.

3. A diaphragm as defined in claim 2 wherein said resin is a resin selected from the group consisting of epoxy, furane, phenolic and melamine.

4. A diaphragm as defined in claim 3 wherein staple pitch fibers represent between about 60% to about by volume of said diaphragm.

5. A diaphragm as defined in claim 1 wherein the sonic velocity of said diaphragm is greater than about 4.6 X 10 cm/sec.

6. A diaphragm as defined in claim 1 having a thickness between about 0.005 inches and about 0.025 inches.

7. A diaphragm as defined in claim 1 wherein said loudspeaker is an electrostatic loudspeaker.

8. A diaphragm as defined in claim 11 having a thickness between about 0.005 inches and about 0.010 inches.

9. A diaphragm as defined in claim 8 wherein said thickness is about 0.007 inches.

10. A diaphragm as defined in claim 1 wherein said carbon fibers represent between about 60% and about 70% by volume of said diaphragm.

11. A diaphragm as defined in claim 5 wherein said sonic velocity is greater than about 10 X 10 cm/sec.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,930,130 Issue Date December 30, 1975 Inventoflg) Samuel M. Boszor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the front page of the patent, after the list of U. S. Patents cited, add the following:

--Foreign Paterts or Applications 48/25515 4/1973 Japan (Early Disclosure Application) At column 10, claim 8, line 38, delete "11" and substitute therefor 7 Engned and Scaled this eighteenth Day of May 1976 [SEAL] Arrest.

RUTH C. M ASQN C. MARSHALL DANN Atlesring Officer Commissioner uflalems and Trademarks a NO- 3,930, Issue Date 30, InventoflK) Samuel M. Boszor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: a I

FD On the front page of the patent, after the list of r U. S. Patents cited, add the following:

--Foreign Paterts or Applications 48/2515 4/1973 Japan 9 (Early Disclosure Application) At column 10, claim 8, line 38, delete "11" and substitute therefor 7 Signed and Scaled this a eighteenth D3) Of May 1976 [SEAL] Arrest:

RUTH C.MASON c. MARSHALL DANN Arresting Officer Commissioner nj'latenls and Trademarks 

1. A LOUDSPEAKER DIAPHRAGM, SAID DIAPHRAGM CONSISTING ESSENTIALLY OF A CARBONACEOUS FIBROUS WEB OF CARBON FIBERS AND A RESIN, SAID CARBON FIBERS REPRESENTING BETWEEN ABOUT 30% AND ABOUT 70% BY VOLUME OF SAID DIAPHRAGM, THE BALANCE BEING SAID RESIN, SAID DIAPHRAGM HAVING A YOUND''S MODULUS BETWEEN ABOUT 3 MILLION PSI AND ABOUT 30 MILLIONS PSI AND A DENSITY BETWEEN ABOUT 0.8 GM/CM2 AND ABOUT 1.7 GM/CM3 SO AS TO PROVIDE A SONIC VELOCITY FOR SAID DIAPHRAGM BETWEEN ABOUT 2.5 X 10**5 CM/SEC AND ABOUT 11 X 10**5 CM/SEC.
 2. A diaphragm as defined in claim 1 wherein said carbon fibers are staple carbon fibers.
 3. A diaphragm as defined in claim 2 wherein said resin is a resin selected from the group consisting of epoxy, furane, phenolic and melamine.
 4. A diaphragm as defined in claim 3 wherein staple pitch fibers represent between about 60% to about 70% by volume of said diaphragm.
 5. A diaphragm as defined in claim 1 wherein the sonic velocity of said diaphragm is greater than about 4.6 X 105 cm/sec.
 6. A diaphragm as defined in claim 1 having a thickness between about 0.005 inches and about 0.025 inches.
 7. A diaphragm as defined in claim 1 wherein said loudspeaker is an electrostatic loudspeaker.
 8. A diaphragm as defined in claim 11 having a thickness between about 0.005 inches and about 0.010 inches.
 9. A diaphragm as defined in claim 8 wherein said thickness is about 0.007 inches.
 10. A diaphragm as defined in claim 1 wherein said carbon fibers represent between about 60% and about 70% by volume of said diaphragm.
 11. A diaphragm as defined in claim 5 wherein said sonic velocity is greater than about 10 X 105 cm/sec. 